The outer bark is the tree's protection from the outside world. Continually renewed from within, it helps keep out moisture in the rain, and prevents the tree from losing moisture when the air is dry. It insulates against cold and heat and wards off insect enemies.

The inner bark, or “phloem”, is pipeline through which food is passed to the rest of the tree. It lives for only a short time, then dies and turns to cork to become part of the protective outer bark.

The cambium cell layer is the growing part of the trunk. It annually produces new bark and new wood in response to hormones that pass down through the phloem with food from the leaves. These hormones, called “auxins”, stimulate growth in cells. Auxins are produced by leaf buds at the ends of branches as soon as they start growing in spring.

Sapwood is the tree's pipeline for water moving up to the leaves. Sapwood is new wood. As newer rings of sapwood are laid down, inner cells lose their vitality and turn to heartwood.

﻿Heartwood﻿ is the central, supporting pillar of the tree. Although dead, it will not decay or lose strength while the outer layers are intact. A composite of hollow, needle like cellulose fibers bound together by a chemical glue called lignin, it is in many ways as strong as steel. A piece 12” long and 1” by 2” in cross section set vertically can support a weight of twenty tons!

﻿Leaves﻿make food for the tree and this tells us much about their shapes. For example, the narrow needles of a Douglasfir can expose as much as three acres of chlorophyll surface to the sun.

The lobes, leaflets and jagged edges of many broad leaves have their uses, too. They help evaporate the water used in food-building, reduce wind resistance— even provide “drip tips” to shed rain that, left standing, could decay the leaf.

BEST & WORST TREES IN A HURRICANE Flying branches and toppling trees can cause property damage, injuries and even death.

But if you select the right trees, you can minimize damage to your home and save the hassle of insurance claims.After the 2004 hurricane season, author and landscape designer Pamela Crawford teamed up with researcher Barbara Hadsell to study the trees that held up best and worst in the storms. The result was their book, Stormscaping (Color Garden, $29.95)."We were unlucky to be hit by so many hurricanes so fast, but it gave us the opportunity to really learn which trees to avoid," Crawford said. "We updated our data in 2005, and there was very little difference. We had so many reports coming in after 2004 that we found it still was good, strong data."

Here is a list of the best and worst trees to have in your yard during hurricane season.

PINE / EVERGREEN TREESAs a common ornamental conifer tree species, pine trees are planted in thousands of gardens to server as wind shield and landscaping trees. However, there are a few things underground you may not know. They usually develop two kinds of roots. Tap roots are shallow roots which are usually grow in a place near the surface of the soil. Tap roots will live for a long time, and they will constantly replaced by new roots. Pine trees also have some deeper roots which will submerge into the deep side of the soil to get nutrients and water for the tree.Pine trees are great landscaping evergreen trees in a backyard which can provide all-year-long green foliages even in cold winter. However, you should think of the size of the tree when they are fully grown. You should avoid planting them too close to your house in case of being affected by their coarse roots. Most of the pine tree roots are growing vertically into a deep location of the soil instead of expanding horizontally. However, if your foundation already some cracks or cleavages with plenty of water and nutrients, the tree roots will be easily attracted into there. You should choose some correct types of pine trees like Black Hills spruce if you worry about that.If your pine trees already cause some damages on your properties or sewage pipes, you should do some actions for that. You should find out the location where the pine roots cause an issue, and analyze the risk of removal these roots. You should consult some arborists for some professional ideas. Then you should dig around the roots and provide adequate space for sawing. Then it is time to saw the roots near the trunk. Try your best to make the cut clean which will keep the tree to be healthy after the pruning.Attribute Image provided by Ann Harrison [CC-BY-SA-2.0 (http://creativecommons.org/licenses/by-sa/2.0)], via Wikimedia Commons